The present invention pertains to a respiratory flow sensor with at least one measuring transducer for the breathing gas volume flow and with at least one air resistance body in a common flow channel.
A respiratory flow sensor described in DE 196 17 318 A1 has an air resistance body arranged in a flow channel and two measuring transducers designed as temperature sensors. This prior-art device is characterized in that the inflow and outflow areas of the flow channel are provided with a grid each and with a corresponding scattering surface, which is separated therefrom in space. As a result, the flow profile in the flow channel is smoothed and better measurement results may be obtained at the same time for the gas volume flow (xe2x80x9cflowxe2x80x9d) from and/or to the patient.
Even though the measuring transducers used hitherto for respiratory flow measurements are suitable, in principle, for gas volume flow measurements, the measured signal depends strongly on the nonuniform profile of the flow velocity in the flow cross section of the flow channel, especially in the case of hot wire and differential pressure measuring transducers, because greatly different incoming flow conditions with correspondingly different degrees of turbulence may occur in the case of use of a respiratory flow sensor near the patient depending on whether the respiratory flow is from or to the patient and depending on the geometric conditions upstream and downstream of the measuring transducer.
The prior-art possibility of making the flow uniform along a shorter section by means of fine-mesh screens installed in the flow channel with and without scattering surface is linked with the drawbacks of an undesired additional pressure loss and the risk of clogging of the meshes of the screen by condensate drops or sputum.
To overcome the drawbacks of the prior-art arrangement, the object of the present invention is to provide a respiratory flow sensor, which is suitable especially for use near a patient, which covers a broad gas volume flow measuring range, which has a low respiratory flow resistance at the same time and which has a good, reproducible measured signal quality.
According to the invention, a respiratory flow sensor is provided with at least one measuring transducer for the breathing gas volume flow and with at least one air resistance body in a common flow channel. An air resistance body is provided with a blunt end and with an opposite, pointed end. The air resistance body is arranged between the measuring transducer (of which there is at least one) and a patient-side end of the respiratory flow sensor. The pointed end of the air resistance body points toward the measuring transducer.
The solution is particularly suitable for making the flow profile of the gas volume flow exhaled by the patient uniform and for measuring both the inhaled and the exhaled gas volume flows.
A second air resistance body with a pointed end may be arranged between the measuring transducer (of which there is at least one) and the end of the respiratory flow sensor, which end is away from the patient. The pointed end of the second air resistance body also points toward the measuring transducer.
The respiratory flow sensor may be made in one piece with a patient adapter with two legs. The two legs may be pivotable around an axis of rotation and the axis of rotation may be arranged at right angles to the central longitudinal axis of the flow channel. The respiratory flow sensor may have a T-shaped adapter connect to the legs.
The flow channel may narrow from both ends to the measuring transducer (of which there is at least one). The measuring transducer (of which there is at least one), sends a measured signal that is proportional to the breathing gas volume flow flowing through the flow channel. The measuring transducer (of which there is at least one) is selected from the group of ultrasonic, hot wire or differential pressure measuring transducers with or without movable diaphragms.
The first and/or the second air resistance bodies may have a rotationally symmetrical design. A symmetry axis of the air resistance bodies may be made to coincide with the central longitudinal axis of the flow channel. The blunt end of the first air resistance body may have a base in the form of a circle or a regular polygon. Following the pointed end, the second air resistance body first has a cylindrical course with a closure joining it in the form of a rounded truncated cone. A chamfer or a rounding may be provided between the base and the jacket surface of the first air resistance body. A plug may extend essentially in parallel to the central longitudinal axis of the flow channel. The plug may be used to lead out the measured signals of the measuring transducer (of which there is at least one). The distance between the measuring transducer (of which there is at least one) and each of the air resistance bodies may correspond at least to the diameter of the respective air resistance body. The respiratory flow sensor may be equipped with optical windows arranged opposite and in parallel to the central longitudinal axis for spectroscopic radiation through the flow channel and with a breathing gas sampling channel.
A substantial advantage of the respiratory flow sensor according to the present invention is that a gas volume flow measuring range from about 1 L per minute to about 120 L per minute can be covered at a required respiratory flow resistance of about 3.0 mbar at a gas volume flow of 60 L per minute and with a reproducible measured signal quality. The result can be attributed to the special design of the respiratory flow sensor with one or preferably two special air resistance bodies in front of and behind the measuring transducer, of which there is at least one, which air resistance bodies lead to an extensive smoothing of the flow profile in the flow channel for the gas volume flow measuring range. If this smoothing of the flow profile was not performed, different measurement results are obtained for the same gas volume flow depending on the position of the respiration tube connected to the respiratory flow sensor and depending on the position and the size of the particular endotracheal catheter being used.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated.